CVE-2026-73256

Mongoose is an embedded web server and network library. Prior to 7.22, a remote unauthenticated attacker can exploit an HTTP/1.0 reverse-proxy deployment by sending a request with Transfer-Encoding: chunked and conflicting framing. The http_cb() function in src/http.c tests hm.proto.len with an impossible greater-than-eight condition even though mg_http_parse() requires an eight-byte protocol string, so is_http_1_0 is never set. Mongoose consequently processes chunked encoding that an HTTP/1.0 proxy can ignore, enabling request smuggling and unauthorized access or state changes. This issue is fixed in version 7.22.

• CWE-444

• https://github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71Patch
• https://github.com/cesanta/mongoose/pull/3611Issue Tracking, Patch
• https://github.com/cesanta/mongoose/releases/tag/7.22Release Notes
• https://github.com/cesanta/mongoose/security/advisories/GHSA-mgp5-rjrv-h5j3Exploit, Vendor Advisory

Published

Aug 20, 2026

Last Modified

Oct 18, 2026

Status

Analyzed

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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